Unable to delete a To-do item.

I’ve never really used the To-do, so I can tell when it stopped working, I only noticed after today’s upgrade to 8.4.6. My problem is that I have one, and only one, list on my To-do-list, and I can delete it, I also can’t add new items to to-do-list. When I try to delete it it just says “You have insufficient privileges to delete items in this folder.”, the error-message kind of says it all, but I can’t understand why, and I can understand how to fix it. Any tips?
We are on Debian 8.10with Kopano 8.4.6.